Electric switch



Patented Dec. 28, 1948 ELECTRIC SWITCH James Leslie Ashford, London, England, assignor,

by mesne assignments. to International Standard Electric Corporation, New York, N. Y., a

corporation of Delaware Application June 22, 1943, Serial No. 491,753 In Great Britain July 28, 1942 z claims. (ci zoo-112) This invention relates to mercury relay switches. The switch to be described has been -developed primarily for application in a spot Welder control circuit where high speed of response is essential; but it is quite suitableA for other purposes where a relay is required that will control fairly high powers.

Among the advantages of the invention are, that a circuit may be broken or made under load without undue deterioration of its contacts owing to the employment of a mercury break; moreover mercury contamination is reduced to a minimum by arranging mercury to mercury break; that a very rapid response to the coil excitation is obtained compared to the tilting tube type; also, by certain adjustments to the design, the speed of response has been still further increased; and thatthe switch will function satisfactorily at an angle of 45 from the vertical.

The several features of the invention are set out as claims 1 to 10 respectively.

A description will now be given of the accompanying drawing which shows an embodiment of the invention, in which Fig. 1 is a vertical sectional view of my mercury relay switch; and Fig.

`2 is a top plan view of the armature in said Referring to Fig. 1, a sealed glass tube I of substantially cylindrical shape contains a quantity of mercury 2, on which floats a magnetic armature 3 which is also of cylindrical shape fitting closely within the glass tube and being slideable axially of the tube. In a particular case the armature had a wall thickness .05 inch and was spaced from the wall of the glass vessel by a gap of .025 inch. Electrical conductors l and 5, which may be of tungsten, are led into the vessel axially through the opposite end walls and are permanenetly located with their ends in juxtaposition but out o f contact. The lead 4 which rises through the bottom end wall is bare so that it makes contact with the pool of mercury; the descending lead 5 on the other hand is covered with glass for'the greater part of itsl length in order to stop mercury breaking froml the rod. The lower lead 4 carries at its upper end a blob of glass I on which is iixed a -porcelain cup 1 containing a smaller pool 8 of mercury. The bare lower end of the upper lead 5 is permanently immersed in this smaller pool.

The surface tension of thev mercury prevents it from rising up between the armature I and tube I, while the capillary action lifts the mercury in the central bore of the armature. The dimensions of the parts and the iilling of mercury are such that, in the case of a normallyclosed switch the pools 2 and t of mercury are in contact over the lip of the cup 1, so that there is a continuous electrical connection between the leads! and l.

Surrounding the waist of the tube l is an operating coil 9. vWhen this coil is energised, it attracts the armature I upwardly, thus lowering the level of the mercury in the pool 2 and breaking the contact between thetwo pools.

A switch in which the contact is normally broken requires rather less ,mercury in the main pool and needs to be positioned in the coil so that, on excitation, the'armature is depressed into the mercury instead of lifted from it so causing the level to rise until contact is established between the two pools.

In Fig. 2 is shown a cross-section of armature 3 of my switch. The armature is provided with a split I0 to reduce eddy current losses.

The following is a resume of the desirable features of the illustrated designs:

(a) The lead 5 to the cup l is insulated as far as the mercury surface B in order to prevent the current break occurring from this wire.

(b) The armature 3 is split as shown at I0 to reduce circulation of eddy currents.

(c) The clearance between the armature an Vthe walls of tube is large enough to ensure that the armature will not bind but at the same time not be large enough to allow penetration of mercury into this gap. Such penetration is not uniform after each successive operation and prevents the armature from assuming the same position each time. Also dirt may be deposited by the mercury in the gap, causing jamming of the armature.

(d) The clearance between the cup and armature is just sufficient to allow mercury to flow in the gap. This dimension is reduced to a minimum in order firstly to obtain the maximum change in surface level for a given change in displacement, e. g. an armature lift of i/" will allow the mercury level to drop l/2. This high ratio of movement will assist in obtaining high speed of operation. Secondly, a small clearance will allow satisfactory operation of the switch at an angle of as much as 45 from the vertical.

(e) The glassenvelope is exhausted of air and filled lwith an inert gas such as argon to aboutv atmospheric pressure. A pressure of gas will reduce the tendency of the mercury to splash.

(f) The solenoid is not so long that the mercury is within its eld as the mercury appears to heat up under such influence.

(a) The amature is, in its normal position. well inside thc solenoid.

What is claimed is:

1. An electric switch comprising an upstanding cylindrical vessel filled with an inert gas under pressure. a pool oi mercury in the vessel, a conductinglead extending through the bottom end wall of the vessel and into contact with the mercury pool. a piston-like armature of magnetic material in thevessel and of a diameter to have a sumciently close nt therein to prevent the rise ot mercury in the intervening space closely adjacent the side walls thereof, a solenoid surrounding the vessel and positioned above the mercury pool and capable of energization to determine the extent to which the amature is,immersed in the mercury, and an insulating cup member supported on the upper end portion oi.' the said lead and having a diameter to establish a close spaced relation with the internal surface of the armature and a lead through the top end wall of the vessel having an insulating coating extended within the cup and an exposed end immersed in the mercury within said cup.

2. An electric switch as claimed in claim 1 in which the amature is a hollow cylinder and is spilt to break its circular continuity and reduce eddy currents.

JAMES LESLIE ASHFORD.

REFERENCES CITED The following references are of record in the tile of this patent:

UNTI'ED STATES PATENTS Name Larson Dec. 1, 1942 

